Electrical resistance unit



'Patented Oct. 2, 1934 PATENT oFFIXcE MECTRICAL RESISTANCE ".l

David T. Siegel, ilhicagc, El.

Application March 24 This invention relates to improvements in electrical resistance units.

An electrical resistance unit usually consists ci a wire having a desired temperature'coelcient 5 wound on a tube or base, preferably of porcelain, iitted with suitable terminals and surrounded by a suitable covering. The wire is wound around the tube or base either contiguously or at desired spaced intervals. This wire is very thin, usually l@ below No. l0 B d: S gauge. This wire is so thin and ne that it has little, if any physical, strength or resistance. The covering applied to a resistance unit is normally enamel which is red on to the porcelain tube at a high temperature.

' l5 The coemcient of expansion of the te madeof copper or other suitable material is comparatively much greater than the coefficient oi expansion of the porcelain tube, and similarly, upon cooling, the contraction of the terminal is ai) likewise far greater. Consequently upon cooling the fine, thin resistance wire, at the point where the same contacts with the terminal, will have exertedagainst it by reason of the contraction of the copper terminal a pressure or pull far be- 25 yond any physical resistance inherent in said thin v wire, and the part or the wire adjacent to the terminal lying upon or contacting with the porcelain will be subjected to a strain or pull because or the comparative lack of any contraction of the ,porcelain tube.

The result has been that upon contraction, the pull or pressure exerted by the copper terminal against the thin resistance wire has caused the latter to break or be snapped oit, with the conse-= quent result that such resistance unit is wholly 'defective and worthless. The commercial loss entailed by such breaking or the resistance wire has heretofore been a serious commercial problem.

It is therefore the object of my invention to 4gproduce an electical resistance unit `oi! .practical and commercial use and value in which the breaking or severing of the resistance wire is eradicated or practically eliminated without in any manner detracting from the utility oi' a resistance 4,5l unit and without changing or efecting its ap' pearance.

It will be understood that electrical resistance umts are made in a great variety of types and sizes, but the invention as herein set forth is obviously applicable to any type and any size, and l therefore do not limit myself to any particular type or size of electrical resistance units.

In my preferred form I use a wire of very low temperature cceicient, which is wound around a refractory porcelain tube fitted with suitable ter- :i930 Nt. 428.605 (ci. coi-cai ,c

around the same l cover with hard vitreous enamel which is red on at high temperatures.

At or near each terminal a comparatively heavy wire, about a No. 30 B Bz S gauge, is wrapped around the porcelain tube upon the ilne resistance coil wire. This second wire is not designed to form any part of the resistance circuit but it serves to impart physical resistance and strength to the thin wire upon which it is wound so as to overcome the pull exerted by the terminal upon contraction, with the result that that side of the terminal nearest to the Wire remains upon contraction practically xed, the contraction of said terminal and any moving of said terminal on the porcelain tube taking place at the side remote from the resistance wire. The result is that upon contraction the thin resistance coil proper is not snapped oil or broken, with the resulting savingr of great loss and expense due to the elimination of ruined resistance units.

It will be understood that the-aforesaid construction may be applied to similar parts of each end oi the resistance unit, or at any point where contact between the iine wire and a terminal is made.

Other objects of the invention will appear from the following description, directed to the preferred embodiments of the invention, as shown in the drawing forming a part of the specication, the novel features of which are set forth in the appended claims.

In the said drawing,

Fig. 1 is a complete finished electrical resistance unit.

Fig. 2 is a similar view as Fig. l prior to the application of the covering of vitreous enamel or other suitable coating.

Fig. 3 is an enlarged end view broken away of the electrical resistance unit of Fig. 2.

Fig. 4 is a cross-sectional view taken on the line 4 4 of Fig. 3.

Fig. 5 is a view of a. large size of electrical resistance unit prior to the application of vitreous enamel or other suitable covering having terminals of phosphor bronze leads.

Like reference characters are applied to like parts in the various iigures.

The reference character l designates the copper terminals on the resistance unit, in which are provided suitable holes 2 for forming contact. The resistance unit is covered with a coating 3 preferably made ci vitreous enamel which is ilred on to the resistance coil. at a high temperature,

- erence character The thin wire forming the resistance coil is 5 shownin Fig'. 2.v 'Ihis coil 5, obviously, is not shown in Fig. 1, since it is beneath the coating .-7 3. Reference `character 6 designates the comparatively heavy wire wound at or near the terminals at each end of the resistance unit, and 'l indicates the end of the wire 6 leading to and connected with a prong on the copper terminal 1. Reference character 9 designates the end of thev resistance coil proper, 5 forming a contact and completing the circuit with the copper terminals at 8. 10 represents the hollow portion of the porcelain tube and 11 represents a part of the porcelain tube 4. minal of phosphor bronze or other suitable material. 13 represents a wire used to hold the iexible terminals in place.

It will be understood that various changes may be made in form and size and in the application thereto of my invention Without departing from the principle and spirit of the same.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. An electrical resistance unit comprising a tube of refractory material, a ne resistance wire wound about the tube, terminals tted directly on the tube-andabutting with the end strand of the resistance wire, and a reenforcing wire en- 12 represents a exible terveloping the resistance wire adjacent the termil nais the tube and abutting with the end strand of the resistance wire, a reenforcing means superposed upon the resistance Wire adjacent the terminals, and a covering material for the resistance wire. 3. An electrical resistance unit comprising a tube of refractory material, a fme resistance wire wound about the tube, terminals iitted directly on the vtube and abutting with the end strand of the resistance Wire, a reenforcing wire enveloping the resistance wire adjacent the terminals, and a covering material for the resistance wire.

4. The method of making an electrical resistance unit comprising Winding a iine resistance wire upon a tube of refractory material, xing terminals on the tube to receive the ends of the resistance wire, covering the resistance wire adjacent the terminals with reenforcing material, and coating the unit with a covering material.

5. The method of making an electrical resistwire, and coating the unit with a covering materil.

DAVID 'I'. SIEGEL.

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